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Anybody got a rigger they'd recommend in Auckland?

 

Problem I have is a 1975 masthead sloop rig, single spreader, power pole type mast, shakes like a bastard when no sails hoisted

which is a) bloody annoying at night when its windy (like Saturday night in Bon Accord or Sunday when anchored while waiting

for depth at river mouth B) not good for the boat at anytime IMO.

 

I have consulted and been told that I should not worry... but I do because it just doesn't seem right.

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Your rig should have fore and aft lowers, typical of Des' designs. These should stop the mast moving around - are they tight enough?

Closest riggers to you would be Phil Ash at Gulf Harbour, he has done good work for me. They are very busy this time of the year, if you want a check might be best to take Romany around to Gulf Harbour

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Thanks for all replies - I'll try Phil he is closest.

No inner forestay, but mast has a position where I believe one may have been/could go (although we have no foredeck 'chain

plate'), have fore and aft lowers but I'm not sure how tight 'tight enough' is, so I guess it's a simple process to tighten and see what happens.

 

Back stay is wound on pretty tight already.

 

Is there a tool of some kind that you can use to get the same tension or is it just feel and a good eye?

 

Is it possible to over tighten?

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Or you can slack them off, measure a 2m section, retention, measure the stretch. Is it 1x19 stainless wire? Iirc 4mm stretch over a 2m length is 15% break load.

I can check that if you want to use this method. Or if you're in Auckland I have a loos gauge.

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Ok thanks all.

 

IT - thanks for the offer,  I am in Weiti, but I will get a rigger involved. Will investigate buying a guage, but the right tools are partly what you pay the experts for I guess, and in the hands of the in-trained could easily be less than helpful.  

 

I also spoke to a mate who has the same boat (built immediately after by the same boat builder) and he blames a combination of things, although his immediate reaction was to get somebody who knows the beast - an rigger with Townson experience, so that's what I will do.

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Elementary setup general rule is 3 deg rake, 15 % on the caps, fore and aft lowers tight enough to induce prebend not exceeding 1.5d and to eliminate fore and aft pumping going to weather. Mast must be in column, and no S bend induced by the partners.

A harmonic vibration at anchor is most often the topping lift, try changing the tension on it, by reducing main tension etc.

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I would be 99% certain that what you are experiencing is a phenomenon called vortex shedding.

I had exactly the same on the Cav39 which had a rig similar to the one you describe. In a strong breeze,particularly on the beam with no sails set, the wind sets up an oscillation in the spar.

The same thing happens in tall chimneys which is why you will often see a spiral welded to the structure.

To test is this is the case... Next time you have the mast oscillating, hoist the biggest diameter rope you have on board to the masthead and spiral wind it down around the mast. It's a real pain to do this above the spreaders, but... If you can get 6 or 8 spirals down from the mast head to mid way between the boom and the spreaders, the shaking will go away.

Unfortunately, I don't know a permanent solution to voirtex shedding on a yacht mast.

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IT has the right info. Rig tuning seems scarier than it actually is, but it is not hard at all and every sailor should learn a little about it. I had too, because of my saga with the Rig. The problem  with the the shaking is called Mast Pumping. Long term it is a serious issue because it puts stress on the rigging wire and can cause premature failure. In fact, it is the loading /unloading of stress on wire that causes it to eventually fail. So when you have those same stresses at a much higher frequency, then failure is going to be much sooner. There have been the odd story of masts falling down when a Boat has been at rest. Simply because of mast pumping.
The cause of pumping is simply an oscillation of a section of mast between terminations. Placing a bre bend in the mast as suggested by IT is what stops that from happening. Every mast has a possibility of pumping, so the rig is carefully designed to stop that from happening once tuned correctly.
Unless you have a dickhead rigging guy that has no clue how to design, install and tune a rig.

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anybody know what a loos guage costs?

 

I bought one from Harken/Fosters approx 1 year ago. Cost was $356.00 (inc GST). They had to bring it in from the USA for me. But it was the tool I needed to do some serious tweaking on my boat.

 

Couple of things the supplier will need to know if you head off and buy one:-

- Type of rigging, Rod or laid wire. The gauge is different depending on which type .

- Diameter of rigging wire. Loos gauges are made to fit various sizes and you need to get one that fits your wire.

 

a.f.u

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Also the prices vary significantly depending on the range of wire diameter you're using: http://www.westmarine.com/buy/loos-company--rig-tension-gauges--P002_065_001_504

 

It's a shame I didn't know this discussion was going to come up. I could have brought one down with me last week.

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Can you expand a little on that?

From Ivan Dedekam's "Sail and Rig Tuning" book, which I have found to be a great reference/ aide memoir. Page 65.

For 1x19 ss wire, over a 2m sample, every 1mm of elongation is 5% of break load. So 3mm for 15%, 4mm for 20%.

For rod, 1mm elongation over a 2m sample is 7.5% BL, so 2.0mm is 15%.

Measuring should commence with rigging hand tight, on clean rigging screws in good order.

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Agreed, it's rough and ready, but short of strain gauges/load cells, it's pretty good. And not for die formed wire etc.

Most sailors have no idea of the actual rig tensions, or the loads on it. IMO this is a great place to start.

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